1<html lang="en"> 2<head> 3<title>x86 specific memory model extensions for transactional memory - Using the GNU Compiler Collection (GCC)</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Using the GNU Compiler Collection (GCC)"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions"> 9<link rel="prev" href="_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins" title="__atomic Builtins"> 10<link rel="next" href="Object-Size-Checking.html#Object-Size-Checking" title="Object Size Checking"> 11<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 12<!-- 13Copyright (C) 1988-2013 Free Software Foundation, Inc. 14 15Permission is granted to copy, distribute and/or modify this document 16under the terms of the GNU Free Documentation License, Version 1.3 or 17any later version published by the Free Software Foundation; with the 18Invariant Sections being ``Funding Free Software'', the Front-Cover 19Texts being (a) (see below), and with the Back-Cover Texts being (b) 20(see below). A copy of the license is included in the section entitled 21``GNU Free Documentation License''. 22 23(a) The FSF's Front-Cover Text is: 24 25 A GNU Manual 26 27(b) The FSF's Back-Cover Text is: 28 29 You have freedom to copy and modify this GNU Manual, like GNU 30 software. Copies published by the Free Software Foundation raise 31 funds for GNU development.--> 32<meta http-equiv="Content-Style-Type" content="text/css"> 33<style type="text/css"><!-- 34 pre.display { font-family:inherit } 35 pre.format { font-family:inherit } 36 pre.smalldisplay { font-family:inherit; font-size:smaller } 37 pre.smallformat { font-family:inherit; font-size:smaller } 38 pre.smallexample { font-size:smaller } 39 pre.smalllisp { font-size:smaller } 40 span.sc { font-variant:small-caps } 41 span.roman { font-family:serif; font-weight:normal; } 42 span.sansserif { font-family:sans-serif; font-weight:normal; } 43--></style> 44<link rel="stylesheet" type="text/css" href="../cs.css"> 45</head> 46<body> 47<div class="node"> 48<a name="x86-specific-memory-model-extensions-for-transactional-memory"></a> 49<p> 50Next: <a rel="next" accesskey="n" href="Object-Size-Checking.html#Object-Size-Checking">Object Size Checking</a>, 51Previous: <a rel="previous" accesskey="p" href="_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins">__atomic Builtins</a>, 52Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a> 53<hr> 54</div> 55 56<h3 class="section">6.53 x86 specific memory model extensions for transactional memory</h3> 57 58<p>The i386 architecture supports additional memory ordering flags 59to mark lock critical sections for hardware lock elision. 60These must be specified in addition to an existing memory model to 61atomic intrinsics. 62 63 <dl> 64<dt><code>__ATOMIC_HLE_ACQUIRE</code><dd>Start lock elision on a lock variable. 65Memory model must be <code>__ATOMIC_ACQUIRE</code> or stronger. 66<br><dt><code>__ATOMIC_HLE_RELEASE</code><dd>End lock elision on a lock variable. 67Memory model must be <code>__ATOMIC_RELEASE</code> or stronger. 68</dl> 69 70 <p>When a lock acquire fails it's required for good performance to abort 71the transaction quickly. This can be done with a <code>_mm_pause</code> 72 73<pre class="smallexample"> #include <immintrin.h> // For _mm_pause 74 75 /* Acquire lock with lock elision */ 76 while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE)) 77 _mm_pause(); /* Abort failed transaction */ 78 ... 79 /* Free lock with lock elision */ 80 __atomic_clear(&lockvar, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE); 81</pre> 82 </body></html> 83 84